Systems and methods for regulating led currents

ABSTRACT

System and method for regulating one or more currents. The system includes a system controller, an inductor, a first resistor, a switch and a first diode. The system controller includes a first controller terminal and a ground terminal, the system controller being configured to output a drive signal at the first controller terminal. The inductor includes a first inductor terminal and a second inductor terminal, the first inductor terminal being coupled to the ground terminal, the second inductor terminal being coupled to one or more light emitting diodes. The first resistor includes a first resistor terminal and a second resistor terminal, the first resistor terminal being coupled to the ground terminal. The switch is configured to receive the drive signal and coupled to the second resistor terminal. The first diode includes a first diode terminal and a second diode terminal and coupled to the first resistor.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201110415842.X, filed Dec. 8, 2011, commonly assigned, incorporated byreference herein for all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for regulatingcurrents. Merely by way of example, the invention has been applied toregulate currents flowing through light-emitting-diodes (LEDs). But itwould be recognized that the invention has a much broader range ofapplicability.

Light emitting diodes (LEDs) have been widely used in variouselectronics applications. LEDs have been recognized for theirsignificant advantages over other lighting sources, such as incandescentbulbs. For example, such advantages include high efficiency and longlifetime. But, challenges remain for low-power LED applications, such aspoor accuracy of current, low efficiency of light conversion, and largesize of printed-circuit-board (PCB). Poor accuracy of current usuallydecreases the lifetime of LEDs, and low efficiency of light conversionoften increases heat generation, which may also reduce the lifetime ofLEDs.

FIG. 1 is a simplified conventional diagram showing a system for drivingLEDs. The system 100 includes a system controller 102, a snubber circuit116, a transformer 118, a rectifying diode 132, a capacitor 134, one ormore LEDs 136, a power switch 138, a current-sensing resistor 140, andtwo resistors 142 and 144. The system controller 102 includes terminals104, 106, 108, 110, 112 and 114. The snubber circuit 116 includes aresistor 120, a capacitor 122 and a diode 124. The transformer 118includes a primary winding 126, a secondary winding 128 and an auxiliarywinding 130. For example, the power switch 138 is a transistor.

If the switch 138 is closed (e.g., on), a primary current 148 flowsthrough the primary winding 126, the switch 138 and the resistor 140,and the transformer 118 stores energy. The resistor 140 generates acurrent-sensing signal 150 which is detected at the terminal 114 (e.g.,CS). If the switch 138 is open (e.g., off), the energy stored in thetransformer 118 is released to drive the one or more LEDs 136.Information about an output voltage 152 associated with the one or moreLEDs 136 is extracted through the auxiliary winding 130. The auxiliarywinding 130, together with the resistors 142 and 144, generates afeedback signal 146 that is detected at the terminal 106 (e.g., FB).Based on at least the current-sensing signal 150 and the feedback signal146, the system controller 102 outputs a gate drive signal 152 throughthe terminal 112 (e.g., GATE) to drive the switch 138 in order toregulate a current 154 that flows through the one or more LEDs 136.

But the system 100 often has low efficiency in power transfer, and suchlow efficiency usually results from low efficiency of the transformer118 and/or energy loss in the snubber circuit 116. Additionally, manyperipheral devices of the system 100 may not satisfy certainrequirements for the PCB size.

Hence it is highly desirable to improve the techniques of driving LEDs.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for regulatingcurrents. Merely by way of example, the invention has been applied toregulate currents flowing through light-emitting-diodes (LEDs). But itwould be recognized that the invention has a much broader range ofapplicability.

According to one embodiment, a system for regulating one or morecurrents includes a system controller, an inductor, a first resistor, aswitch and a first diode. The system controller includes a firstcontroller terminal and a ground terminal, the system controller beingconfigured to output a drive signal at the first controller terminal.The inductor includes a first inductor terminal and a second inductorterminal, the first inductor terminal being coupled to the groundterminal, the second inductor terminal being coupled to one or morelight emitting diodes. The first resistor includes a first resistorterminal and a second resistor terminal, the first resistor terminalbeing coupled to the ground terminal. The switch is configured toreceive the drive signal and coupled to the second resistor terminal.Moreover, the first diode includes a first diode terminal and a seconddiode terminal and coupled to the first resistor, the second diodeterminal being coupled to the one or more light emitting diodes.

According to another embodiment, a system for regulating one or morecurrents includes a system controller, a transformer, a first resistor,a switch, and a first diode. The system controller includes a firstcontroller terminal and a ground terminal, the system controller beingconfigured to output a drive signal at the first controller terminal.The transformer includes a primary winding and a secondary winding, theprimary winding including a first winding terminal and a second windingterminal, the secondary winding including a third winding terminal and afourth winding terminal, the first winding terminal being coupled to theground terminal, the second winding terminal being coupled to one ormore light emitting diodes, the third winding terminal being coupled tothe ground terminal. The first resistor includes a first resistorterminal and a second resistor terminal, the first resistor terminalbeing coupled to the ground terminal. The switch is configured toreceive the drive signal and coupled to the second resistor terminal.Additionally, the first diode includes a first diode terminal and asecond diode terminal and coupled to the first resistor, the seconddiode terminal being coupled to the one or more light emitting diodes.

According to yet another embodiment, a system for regulating one or morecurrents includes a system controller that is configured to output adrive signal to a switch and to receive a sensed signal from a resistorconnected to the switch and an inductor, the resistor and the inductorbeing connected directly or indirectly to one or more light emittingdiodes. Additionally, the drive signal is associated with one or moreswitching periods, each of the one or more switching periods includingan on-time period for the switch and an off-time period for the switch.Moreover, each of the one or more switching periods is equal to a ratiomultiplied by a demagnetization period for a demagnetization processassociated with the inductor, the ratio being larger than 1.Furthermore, a first current flowing through the one or more lightemitting diodes is proportional to a peak magnitude of the sensed signalwithin each of the one or more switching periods.

According to yet another embodiment, a system for regulating one or morecurrents includes a modulation-and-drive component, a sample-and-holdcomponent, an amplification component, an error amplifier, and acomparator. The modulation-and-drive component is configured to output adrive signal to a switch, the drive signal being associated with atleast one switching period including an on-time period for the switchand a demagnetization period for a demagnetization process. Thesample-and-hold component is configured to receive a sensed signalrelated to a current flowing through the switch, sample the sensedsignal at the middle of the on-time period, and hold the sampled sensedsignal. The amplification component is configured to receive the heldand sampled sensed signal during the demagnetization period and generatean amplified signal. In addition, the error amplifier is configured toreceive the amplified signal during the demagnetization period andgenerate, with at least a first capacitor, an integrated signal.Moreover, the comparator is configured to receive at least theintegrated signal and output a comparison signal to themodulation-and-drive component based on at least information associatedwith the integrated signal.

In another embodiment, a system for regulating one or more currentsincludes a modulation-and-drive component, a signal-holding component,an amplification component, an error amplifier, and a comparator. Themodulation-and-drive component is configured to output a drive signal toa switch, the drive signal being associated with at least one switchingperiod including an on-time period for the switch and a demagnetizationperiod for a demagnetization process. The amplification component isconfigured to, during the demagnetization period, receive a sensedsignal related to a first current flowing through the switch andgenerate an amplified signal. Additionally, the error amplifier isconfigured to receive the amplified signal during the demagnetizationperiod and generate, with at least a first capacitor, an integratedsignal. Moreover, the comparator is configured to receive at least theintegrated signal and output a comparison signal to themodulation-and-drive component based on at least information associatedwith the integrated signal.

In yet another embodiment, a method for regulating one or more currentsincludes receiving a sensed signal from a resistor connected to a switchand an inductor, and processing information associated with the sensedsignal. In addition, the method includes generating a drive signal forthe switch based on at least information associated with the sensedsignal, processing information associated with the drive signal, andgenerating a current flowing through one or more light emitting diodesbased on at least information associated with the drive signal, the oneor more light emitting diodes being connected directly or indirectly tothe resistor and the inductor. Further, the drive signal is associatedwith one or more switching periods, each of the one or more switchingperiods including an on-time period for the switch and an off-timeperiod for the switch. Each of the one or more switching periods isequal to a ratio multiplied by a demagnetization period for ademagnetization process associated with the inductor, the ratio beinglarger than 1. Moreover, the current is proportional to a peak magnitudeof the sensed signal within each of the one or more switching periods.

In yet another embodiment, a method for regulating one or more currentsincludes generating a drive signal for a switch, the drive signal beingassociated with at least one switching period including an on-timeperiod for the switch and a demagnetization period for a demagnetizationprocess. The method further includes receiving a sensed signal relatedto a current flowing through the switch, processing informationassociated with the sensed signal, and sampling the sensed signal at themiddle of the on-time period. In addition, the method includes holdingthe sampled sensed signal, receiving the held and sampled sensed signalduring the demagnetization period, and processing information associatedwith the received held and sampled sensed signal. The method alsoincludes generating an amplified signal based on at least informationassociated with the received held and sampled sensed signal, receivingthe amplified signal, and processing information associated with theamplified signal. Furthermore, the method includes generating anintegrated signal based on at least information associated with theamplified signal, receiving at least the integrated signal, processinginformation associated with the integrated signal, and generating acomparison signal based on at least information associated with theintegrated signal.

In yet another embodiment, a method for regulating one or more currentsincludes generating a drive signal for a switch, the drive signal beingassociated with at least one switching period including an on-timeperiod for the switch and a demagnetization period for a demagnetizationprocess. Additionally, the method includes receiving a sensed signalrelated to a current flowing through the switch during thedemagnetization period, processing information associated with thereceived sensed signal, and generating an amplified signal based oninformation associated with the received sensed signal. The method alsoincludes receiving the amplified signal, processing informationassociated with the amplified signal, and generating an integratedsignal based on at least information associated with the amplifiedsignal. Moreover, the method includes receiving at least the integratedsignal, processing information associated with the integrated signal,generating a comparison signal based on at least information associatedwith the integrated signal, and receiving the comparison signal.

Depending upon embodiment, one or more benefits may be achieved. Thesebenefits and various additional objects, features and advantages of thepresent invention can be fully appreciated with reference to thedetailed description and accompanying drawings that follow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified conventional diagram showing a system for drivingLEDs.

FIG. 2 is a simplified diagram showing a system for driving LEDsaccording to one embodiment of the present invention.

FIG. 3(a) is a simplified diagram showing certain components of a systemcontroller for driving LEDs according to one embodiment of the presentinvention.

FIG. 3(b) is a simplified timing diagram for the system controlleraccording to one embodiment of the present invention.

FIG. 4(a) is a simplified diagram showing certain components of a systemcontroller for driving LEDs according to another embodiment of thepresent invention.

FIG. 4(b) is a simplified timing diagram for the system controlleraccording to another embodiment of the present invention.

FIG. 5 is a simplified diagram showing a system for driving LEDsaccording to another embodiment of the present invention.

FIG. 6 is a simplified diagram showing a system for driving LEDsaccording to yet another embodiment of the present invention.

FIG. 7 is a simplified diagram showing a system for driving LEDsaccording to yet another embodiment of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for regulatingcurrents. Merely by way of example, the invention has been applied toregulate currents flowing through light-emitting-diodes (LEDs). But itwould be recognized that the invention has a much broader range ofapplicability.

FIG. 2 is a simplified diagram showing a system for driving LEDsaccording to one embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The system 200 includes a regulation circuit 201, arectifying-and-filtering circuit 204, and a buck-boost switching circuit206. The rectifying-and-filtering circuit 204 includes a fuse 208, avaristor 210, a common-mode filtering inductor 212, two X capacitors 214and 216, a rectifying bridge 218, and a filtering capacitor 220. Thebuck-boost switching circuit 206 includes a buck-boost inductor 222, aswitch 224, a fly-back diode 226, a filtering capacitor 228, acurrent-sensing resistor 230, and an output dummy resistor 232. Theregulation circuit 201 includes a system controller 202, threecapacitors 234, 236 and 238, five resistors 240, 242, 244, 246 and 248,two diodes 250 and 252, and a Zener diode 254. The system controller 202includes six terminals 260, 262, 264, 266, 268 and 270.

For example, different terminals of the system controller 202 are usedfor different purposes. Table 1 shows, as an example, description of theterminals in the system controller 202.

TABLE 1 Terminals Terminal Name Description 260 GND Controller or Chipground 262 GATE Gate drive 264 CS Current sensing input 266 VDD Powersupply input 268 COMP Control loop compensation 270 FB Output voltagefeedback

In another example, a terminal of the resistor 230 and a terminal of theinductor 222 are each coupled to a chip ground 272 (e.g., a controllerground). The chip ground 272 may be referred to as ground hereinafter.In yet another example, loop compensation is carried out internally inthe system controller 202. In yet another example, the terminal 268(e.g., COMP) is omitted. In yet another example, the switch 224 is atransistor.

According to one embodiment, the inductor 222 (e.g., L2) has oneterminal coupled to the chip ground 272 and the other terminal coupledto one or more LEDs 280. For example, the resistor 230 (e.g., R7) hasone terminal coupled to the chip ground 272, and the other terminalcoupled to the switch 224. In another example, the diode 226 (e.g., D1)has one terminal (e.g., a cathode terminal) coupled to the resistor 230,and the other terminal (e.g., an anode terminal) coupled to the one ormore LEDs 280. In yet another example, the terminal 264 (e.g., CS) iscoupled to the chip ground 272 through the capacitor 238 (e.g., C5), andcoupled to both the resistor 230 (e.g., R7) and the switch 224 throughthe resistor 248 (e.g., R5). In yet another example, the terminal 270(e.g., FB) is coupled to the chip ground 272 through the resistor 246(e.g., R4), and coupled to the inductor 222 (e.g., L2) through theresistor 244 (e.g., R3) and the diode 252 (e.g., D3). In yet anotherexample, the terminal 262 (e.g., GATE) is coupled to the switch 224(e.g., at a gate terminal of the switch 224). In yet another example,the terminal 260 (e.g., GND) is coupled to the chip ground 272. Theresistor 248 (e.g., R5) and the capacitor 238 (e.g., C5) are omitted insome embodiments.

According to another embodiment, an AC input 274 is applied to therectifying-and-filtering circuit 204, which generates an input signal276. For example, the regulation circuit 201 receives the input signal276, and outputs a gate drive signal 288 through the terminal 262 (e.g.,GATE) to drive the switch 224. In another example, the buck-boostswitching circuit 206 receives the input signal 276 for driving the oneor more LEDs 280. In yet another example, a switching period of thesystem 200 includes an on-time period, T_(on), during which the switch224 is closed (e.g., on), and an off-time period, T_(off), during whichthe switch 224 is open (e.g., off).

According to yet another embodiment, when the switch 224 is closed(e.g., on), a current 278 flows through the resistor 230 and theinductor 222. For example, the inductor 222 stores energy. In anotherexample, a voltage signal 290 is generated by the resistor 230. In yetanother example, the voltage signal 290 is proportional in magnitude tothe product of the current 278 and the resistance of the resistor 230.In yet another example, the voltage signal 290 is detected at theterminal 264 (e.g., CS) through the resistor 248.

When the switch 224 is open (e.g., off), the off-time period T_(off)begins, and a demagnetization process of the inductor 222 startsaccording to some embodiments. For example, at least part of the current278 flows from the inductor 222 to the one or more LEDs 280 and flowsthrough the diode 226. In another example, the resistor 232 has a largeresistance, and a current 284 that flows through the one or more LEDs280 is close, in magnitude, to the current 278. In yet another example,an output voltage signal 286 associated with the one or more LEDs 280 isdetected at the terminal 270 (e.g., FB) through a resistor divider thatincludes the resistor 244 and the resistor 246. In yet another example,the voltage signal 286 is higher than the voltage of the chip ground 272during the demagnetization process of the inductor 222. In yet anotherexample, after the demagnetization process of the inductor 222 iscompleted, the voltage signal 286 decreases to a low value in magnitude.In yet another example, the system 200 operates with a broad range ofinputs and output loads, such as an input range of AC 85V˜264V, and anoutput load of three or more LEDs.

In another embodiment, the peak value of the current 278 in eachswitching period of the system 200 is kept approximately constant bymonitoring the voltage signal 290 through the terminal 264 (e.g., CS).For example, the demagnetization period of the inductor 222 is detectedby monitoring the voltage signal 286 through the terminal 270 (e.g.,FB). In another example, a switching period of the system 200 is N timesthe demagnetization period of the inductor 222, where N is a ratiolarger than 1. Thus, an average magnitude of the current 284 that flowsthrough the one or more LEDs 280 can be determined based on thefollowing equation according to certain embodiments:

$\begin{matrix}{I_{LED} = {\frac{1}{2 \times N} \times \frac{V_{{TH}\; \_ \; {OC}}}{R\; 7}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

where km represents the average magnitude of the current 284 that flowsthrough the one or more LEDs 280, N represents the ratio between theswitching period of the system 200 and the demagnetization period of theinductor 222, V_(TH_OC) represents the peak value of the voltage signal290, and R7 represents the resistance of the resistor 230.

FIG. 3(a) is a simplified diagram showing certain components of a systemcontroller for driving LEDs according to one embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications.

The system controller 300 includes a timing component 302, threeswitches 304, 306 and 308, a gain stage 310 (e.g., an amplifyingcomponent), an amplifier 312, a comparator 314, anoscillating-and-jittering component 316, a flip-flop 318, a logiccontrol component 320, a gate drive component 322, anover-current-protection (OCP) component 324, a leading-edge-blanking(LEB) component 326, a reference-signal generator 328, a voltage-signalgenerator 330, an output over-voltage-protection (OVP) component 332, ademagnetization detector 334, and a capacitor 336. In addition, thesystem controller 300 includes terminals 360, 362, 364, 366, 368 and370. For example, the system controller 300 is the same as the systemcontroller 202. In another example, the terminals 360, 362, 364, 366,368 and 370 are the same as the terminals 260, 262, 264, 266, 268 and270, respectively. In yet another example, the amplifier 312 includes anoperational transconductance amplifier. In yet another example, theamplifier 312 and a capacitor 392 are included in an integrator.

According to one embodiment, the system controller 300 is used toreplace the system controller 202 as part of the system 200. Forexample, a current-sensing signal 390 that is associated with a current(e.g., the current 278) flowing through the inductor 222 and theresistor 230 is received at the terminal 364 (e.g., CS). In anotherexample, the timing component 302 generates a timing signal 338 to closethe switch 304 for a predetermined period of time during the on-timeperiod T_(on) to sample the signal 390. In yet another example, adetection signal 340 is stored on the capacitor 336. In yet anotherexample, as the signal 390 increases in magnitude during thepredetermined period of time, the detection signal 340 increases inmagnitude. In yet another example, the switch 304 is opened (e.g., off)immediately after the predetermined period of time (e.g., at themidpoint of the on-time period T_(on)). Thus, the current-sensing signal390 is sampled (e.g., at the midpoint of the on-time period T_(on)), andthe sampled signal is then held (e.g., stored) on the capacitor 336according to certain embodiments.

In another embodiment, the demagnetization component 334 receives at theterminal 370 (e.g., FB) a feedback signal 386 that is associated with anoutput voltage signal (e.g., the signal 286) associated with the one ormore LEDs 280. For example, the feedback signal 386 is related to ademagnetization process of the inductor 222. In another example, inresponse, the demagnetization component 334 outputs a demagnetizationsignal 342 and a complementary signal 344. In yet another example,during the demagnetization process of the inductor 222, thedemagnetization signal 342 is at a logic high level and thecomplementary signal 344 is at a logic low level. In yet anotherexample, after the demagnetization process of the inductor 222 ends, thedemagnetization signal 342 is at the logic low level and thecomplementary signal 344 is at the logic high level.

According to yet another embodiment, if the demagnetization signal 342is at the logic high level and the complementary signal 344 is at thelogic low level, the switch 306 is closed (e.g., on) and the switch 308is open (e.g., off). For example, the gain stage 310 receives the storeddetection signal 340 through the switch 306 and outputs an amplifiedsignal 346 to the amplifier 312. In another example, the amplifier 312receives a reference signal 348 (e.g., V_(ref)) from thereference-signal generator 328. In yet another example, the amplifier312, in response, generates an integrated signal 350 with the capacitor392, based on the amplified signal 346 and the reference signal 348. Inyet another example, the comparator 314 receives the integrated signal350 and a ramping signal 352 from the oscillating-and-jitteringcomponent 316, and generates a comparison signal 354. In yet anotherexample, the flip-flop 318 receives the comparison signal 354 and aclock signal 356 from the oscillating-and-jittering component 316, andoutputs a modulation signal 358 to the logic control component 320. Inyet another example, the logic control component 320 also receives asignal 373 from the output OVP component 332, two signals 374 and 376from the voltage-signal generator 330, and a signal 380 from the OCPcomponent 324. In yet another example, in response, the logic controlcomponent 320 outputs a signal 378 to the gate drive component 322 toaffect an on-time period of the switch 224. In yet another example, thesignal 378 is a pulse-width-modulation (PWM) signal. An average currentof the one or more LEDs 280 is proportional to an average current of theinductor 222 during a demagnetization process of the inductor 222 by apredetermined ratio (e.g., the predetermined ratio being equal to 1)according to certain embodiments. For example, the average current ofthe one or more LEDs 280 can be determined according to the followingequation:

$\begin{matrix}{I_{LED} = \frac{V_{ref}}{R\; 7*G}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

where I_(LED) represents the average current of the one or more LEDs280, V_(ref) represents the reference signal 348, R7 represents theresistance of the resistor 230, and G represents a gain of the gainstage 310. In another example, the average current of the one or moreLEDs 280 is constant in magnitude.

In another embodiment, if the demagnetization signal 342 is at the logiclow level and the complementary signal 344 is at the logic high level,the switch 306 is open (e.g., off) and the switch 308 is closed (e.g.,on). For example, the gain stage 310 receives a signal 382 (e.g., 0 V)from a chip ground 372.

FIG. 3(b) is a simplified timing diagram for the system controller 300according to one embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The waveform 301 represents the feedback signal 386 as a function oftime, the waveform 303 represents the current that flows through theinductor 222 as a function of time, and the waveform 305 represents thecurrent-sensing signal 390 as a function of time. Additionally, thewaveform 307 represents the timing signal 338 as a function of time, thewaveform 309 represents the modulation signal 358 as a function of time,and the waveform 311 represents the detection signal 340 as a functionof time. Furthermore, the waveform 313 represents the demagnetizationsignal 342 as a function of time, and the waveform 315 represents theintegrated signal 350 as a function of time.

Five time periods T_(on1), T_(half), T_(off1), T_(demag1) and T_(s1) areshown in FIG. 3(b). The time period T_(on1) starts at time to and endsat time t₂, the time period T_(half) starts at the time to and ends attime t₁, and the time period T_(off1) starts at the time t₂ and ends attime t₄. In addition, the time period T_(demag1) starts at the time t₂and ends at time t₃, and the time period T_(s1) starts at the time toand ends at the time t₄. For example, t₀≤t₁≤t₂≤t₃≤t₄. In anotherexample, t₁ is at the midpoint of the time period T_(on1). In yetanother example, T_(half) is equal to half of T_(on1) (e.g., T_(half)=½T_(on1)).

According to one embodiment, the time period T_(on1) represents theon-time period during which the switch 224 is closed (e.g., on). Forexample, the time period T_(off1) represents the off-time period duringwhich the switch 224 is open (e.g., off). In another example, the timeperiod T_(demag1) represents the demagnetization period of the inductor222. In yet another example, the time period T_(s1) represents theswitching period of the system 200. In yet another example, the timeperiod T_(s1) includes the time period T_(on1) and the time periodT_(off1). In yet another example, the time period T_(on1) includes thetime period T_(half). In yet another example, the time period T_(off1)includes the time period T_(demag1).

According to another embodiment, at the beginning of the time periodT_(on1) (e.g., at to), the switch 224 is closed (e.g., on). For example,the current (e.g., the current 278) that flows through the inductor 222increases in magnitude (e.g., as shown by the waveform 303). In anotherexample, the current-sensing signal 390 increases in magnitude (e.g., asshown by the waveform 305). In yet another example, the timing signal338 changes from a logic low level to a logic high level (e.g., as shownby the waveform 307), and the switch 304 is closed (e.g., on). In yetanother example, the detection signal 340 decreases, in magnitude, froma previous value 325 to a low value 327 (e.g., 0) as shown by thewaveform 311. In yet another example, the feedback signal 386 decreasesto a low value 335 (e.g., 0) as shown by the waveform 301. In yetanother example, the demagnetization signal 342 is at a logic low level(e.g., as shown by the waveform 313), and the switch 306 is open (e.g.,off). In yet another example, the modulation signal 358 changes from thelogic low level to the logic high level (e.g., as shown by the waveform309).

According to yet another embodiment, during the time period T_(half),the current that flows through the inductor 222 continues to increase inmagnitude (e.g., as shown by the waveform 303). For example, thecurrent-sensing signal 390 continues to increase in magnitude (e.g., asshown by the waveform 305). In another example, the timing signal 338keeps at the logic high level (e.g., as shown by the waveform 307), andthe switch 304 is closed (e.g., on). In yet another example, thedetection signal 340 increases in magnitude to a peak value 317 (e.g.,at t₁) as shown by the waveform 311. In yet another example, thefeedback signal 386 keeps at the low value 335 (e.g., 0) as shown by thewaveform 301. In yet another example, the demagnetization signal 342keeps at the logic low level (e.g., as shown by the waveform 313), andthe switch 306 is open (e.g., off). In yet another example, themodulation signal 358 keeps at the logic high level (e.g., as shown bythe waveform 309) during the time period T_(half). In yet anotherexample, at the end of the time period T_(half) (e.g., t₁), the timingsignal 338 changes from the logic high level to the logic low level(e.g., as shown by the waveform 307), and the switch 304 is open (e.g.,off).

According to yet another embodiment, during the rest of the time periodT_(on1) (e.g., after t₁), the detection signal 340 that is stored at thecapacitor 336 keeps at the peak value 317 (e.g., V_(cs_1/2Ton)). Forexample, the feedback signal 386 keeps at the low value 335 (e.g., 0) asshown by the waveform 301. In another example, the demagnetizationsignal 342 keeps at the logic low level (e.g., as shown by the waveform313), and the switch 306 remains open (e.g., off). In yet anotherexample, the modulation signal 358 keeps at the logic high level (e.g.,as shown by the waveform 309). In yet another example, the current thatflows through the inductor 222 continues to increase in magnitude to apeak value 331 (e.g., at t₂) as shown by the waveform 303. In yetanother example, the current-sensing signal 390 continues to increase inmagnitude to a value 333 (e.g., at t₂) as shown by the waveform 305. Inyet another example, the peak value 317 of the detection signal 340 isequal to half of the peak value 333 of the current-sensing signal 390.

According to yet another embodiment, at the beginning of the time periodT_(on1) (e.g., at t₂), the switch 224 is open (e.g., off). For example,at least part of the current (e.g., the current 278) flows from theinductor 222 to the one or more LEDs 280. In another example, thefeedback signal 386 changes from the low value 335 (e.g., 0) to a highvalue 329 (e.g., at t₂) as shown by the waveform 301. In yet anotherexample, the demagnetization signal 342 changes from the logic low levelto the logic high level (e.g., as shown by the waveform 313), whichindicates that the demagnetization process of the inductor 222 starts.In yet another example, the switch 306 is closed (e.g., on). In anotherexample, the gain stage 310 receives the stored detection signal 340,and outputs the amplified signal 346 to the amplifier 312 that outputsthe integrated signal 350. In yet another example, the modulation signal358 changes from the logic high level to the logic low level (e.g., asshown by the waveform 309).

According to yet another embodiment, during the time period T_(demag1),the inductor 222 demagnetizes. For example, the magnitude of thefeedback signal 386 is kept higher than the low value 335 as shown bythe waveform 301. In another example, the current (e.g., the current278) that flows through the inductor 222 and the resistor 230 decreasesin magnitude to a low value 321 (e.g., as shown by the waveform 303). Inyet another example, the current-sensing signal 390 decreases inmagnitude to a low value 323 (e.g., as shown by the waveform 305). Inyet another example, the timing signal 338 keeps at the logic low level,and the switch 304 remains open (e.g., off). In yet another example, thedetection signal 340 keeps at the peak value 317 (e.g., as shown by thewaveform 311). In yet another example, the demagnetization signal 342keeps at the logic high level (e.g., as shown by the waveform 313), andthe switch 306 remains closed (e.g., on). In yet another example, theintegrated signal 350 keeps approximately at a magnitude 319 with asmall fluctuation (e.g., as shown by the waveform 315). In yet anotherexample, the modulation signal 358 keeps at the logic low level (e.g.,as shown by the waveform 309) during the time period T_(demag1). At theend of the time period T_(demag1), the feedback signal 386 abruptlydrops in magnitude as shown by the waveform 301, according to certainembodiments. For example, the demagnetization period of the inductor 222is detected by monitoring the feedback signal 386 at the terminal 270(e.g., FB).

In another embodiment, during the rest of the time period T_(on1) (e.g.,after the demagnetization process of the inductor 222 ends at t₃), thecurrent that flows through the inductor 222 keeps at the low value 321(e.g., as shown by the waveform 303). For example, the current-sensingsignal 390 keeps at the low value 323 (e.g., as shown by the waveform305). In another example, the timing signal 338 remains at the logic lowlevel (e.g., as shown by the waveform 307), and the switch 304 remainsopen (e.g., off). In yet another example, the detection signal 340 keepsat the peak value 317 (e.g., as shown by the waveform 311). In yetanother example, the demagnetization signal 342 keeps at the logic highlevel (e.g., as shown by the waveform 313). In yet another example, theintegrated signal 350 keeps approximately at the magnitude 319 with asmall fluctuation (e.g., as shown by the waveform 315). In yet anotherexample, the modulation signal 358 keeps at the logic low level (e.g.,as shown by the waveform 309).

At the beginning of a next switching period (e.g., at t₄), a new cyclestarts according to certain embodiments. For example, the current thatflows through the inductor 222 increases in magnitude (e.g., as shown bythe waveform 303), and the current-sensing signal 390 increases inmagnitude again (e.g., at t₄ as shown by the waveform 305). In anotherexample, the timing signal 338 changes from the logic low level to thelogic high level (e.g., at t₄ as shown by the waveform 307), and theswitch 304 is closed (e.g., on) to sample the current-sensing signal 390again. In yet another example, the integrated signal 350 keepsapproximately at the magnitude 319 with a small fluctuation (e.g., asshown by the waveform 315) during the next switching period (e.g.,because of a very limited loop bandwidth).

FIG. 4(a) is a simplified diagram showing certain components of a systemcontroller for driving LEDs according to another embodiment of thepresent invention. This diagram is merely an example, which should notunduly limit the scope of the claims. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications.

The system controller 400 includes two switches 406 and 408, a gainstage 410 (e.g., an amplifying component), an amplifier 412, acomparator 414, an oscillating-and-jittering component 416, a flip-flop418, a logic control component 420, a gate drive component 422, an OCPcomponent 424, a LEB component 426, a reference-signal generator 428, avoltage-signal generator 430, an output OVP component 432, ademagnetization detector 434, and a capacitor 436. In addition, thesystem controller 400 includes terminals 460, 462, 464, 466, 468 and470. For example, the system controller 400 is the same as the systemcontroller 202. In another example, the terminals 460, 462, 464, 466,468 and 470 are the same as 260, 262, 264, 266, 268 and 270,respectively. In yet another example, the amplifier 412 includes anoperational transconductance amplifier. In yet another example, theamplifier 412 and a capacitor 492 are included in an integrator.

According to one embodiment, the system controller 400 is used toreplace the system controller 202 as part of the system 200. Forexample, a current-sensing signal 490 that is associated with a current(e.g., the current 278) that flows through the inductor 222 and theresistor 230 is received at the terminal 464 (e.g., CS). In anotherexample, the signal 490 is stored at the capacitor 436. In yet anotherexample, the demagnetization component 434 receives at the terminal 470(e.g., FB) a feedback signal 486 that is associated with an outputvoltage signal (e.g., the signal 286) associated with the one or moreLEDs 280. In yet another example, the feedback signal 486 is related toa demagnetization process of the inductor 222. In yet another example,in response, the demagnetization component 434 outputs a demagnetizationsignal 442 and a complementary signal 444. In another example, duringthe demagnetization process of the inductor 222, the demagnetizationsignal 442 is at a logic high level and the complementary signal 444 isat a logic low level. In yet another example, after the demagnetizationprocess of the inductor 222 ends, the demagnetization signal 442 is atthe logic low level and the complementary signal 444 is at the logichigh level. The capacitor 436 is removed in some embodiments.

According to another embodiment, if the demagnetization signal 442 is atthe logic high level and the complementary signal 444 is at the logiclow level, the switch 406 is closed (e.g., on) and the switch 408 isopen (e.g., off). For example, the gain stage 410 receives the signal490 (or the stored signal 490) through the switch 406 and outputs anamplified signal 446. In another example, the amplifier 412 receives theamplified signal 446, and a reference signal 448 (e.g., V_(ref)) fromthe reference-signal generator 428. In yet another example, theamplifier 412, in response, generates an integrated signal 450 with thecapacitor 492, based on the amplified signal 446 and the referencesignal 448. In yet another example, the comparator 414 receives theintegrated signal 450, and a ramping signal 452 from theoscillating-and-jittering component 416. In yet another example, thecomparator 414 outputs a comparison signal 454. In yet another example,the flip-flop 418 receives the comparison signal 454 and a clock signal456 from the oscillating-and-jittering component 416, and outputs amodulation signal 458 to the logic control component 420. In yet anotherexample, the logic control component 420 also receives a signal 473 fromthe output OVP component 432, two signals 474 and 476 from thevoltage-signal generator 430, and a signal 480 from the OCP component424. In yet another example, in response, the logic control component420 outputs a signal 478 to the gate drive component 422 to affect anon-time period of the switch 224. In yet another example, the signal 478is a PWM signal. An average current of the one or more LEDs 280 isproportional to an average current of the inductor 222 during ademagnetization process of the inductor 222 by a predetermined ratio(e.g., the predetermined ratio being equal to 1) according to certainembodiments. For example, the average current of the one or more LEDs280 can be determined according to the following equation:

$\begin{matrix}{I_{LED} = \frac{V_{ref}}{R\; 7*G}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

where I_(LED) represents the average current of the one or more LEDs280, V_(ref) represents the reference signal 448, R7 represents theresistance of the resistor 230, and G represents a gain of the gainstage 410. In another example, the average current of the one or moreLEDs 280 is constant in magnitude. In yet another example, if G equals1, the gain stage 410 is omitted.

In another embodiment, if the complementary signal 444 is at the logichigh level and the demagnetization signal 442 is at the logic low level,the switch 408 is closed (e.g., on) and the switch 406 is open (e.g.,off). For example, the gain stage 410 receives a signal 482 (e.g., 0 V)from a chip ground 472.

FIG. 4(b) is a simplified timing diagram for the system controller 400according to another embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The waveform 401 represents the feedback signal 486 as a function oftime, the waveform 403 represents the current that flows through theinductor 222 as a function of time, and the waveform 405 represents thecurrent-sensing signal 490 as a function of time. Additionally, thewaveform 407 represents the modulation signal 458 as a function of time,and the waveform 409 represents the demagnetization signal 442 as afunction of time, and the waveform 411 represents the integrated signal450 as a function of time.

Four time periods T_(on2), T_(off2), T_(demag2) and T_(s2) are shown inFIG. 4(b). The time period T_(on2) starts at time t₅ and ends at timet₆, the time period T_(off2) starts at the time t₆ and ends at time t₈,and the time period T_(demag2) starts at the time t₆ and ends at timet₇, and the time period T_(s2) starts at the time t₅ and ends at thetime t₈. For example, t₅≤t₆≤t₇≤t₈.

According to one embodiment, the time period T_(on2) represents theon-time period during which the switch 224 is closed (e.g., on). Forexample, the time period T_(off2) represents the off-time period duringwhich the switch 224 is open (e.g., off). In another example, the timeperiod T_(demag2) represents the demagnetization period of the inductor222. In yet another example, the time period T_(s2) represents theswitching period of the system 200. In yet another example, the timeperiod T_(s2) includes the time period T_(on2) and the time periodT_(off2). In yet another example, the time period T_(off2) includes thetime period T_(demag2).

According to another embodiment, at the beginning of the time periodT_(on2) (e.g., at t₅), the switch 224 is closed (e.g., on). For example,the current (e.g., the current 278) that flows through the inductor 222increases in magnitude (e.g., as shown by the waveform 403). In anotherexample, the current-sensing signal 490 increases in magnitude (e.g., asshown by the waveform 405). In yet another example, the feedback signal486 decreases to a low value 419 (e.g., 0 at t₅) as shown by thewaveform 401. In yet another example, the demagnetization signal 442 isat a logic low level (e.g., as shown by the waveform 409), and theswitch 406 is open (e.g., off). In yet another example, the modulationsignal 458 changes from a logic low level to a logic high level (e.g.,as shown by the waveform 407).

According to yet another embodiment, during the time period T_(on2), thecurrent (e.g., the current 278) that flows through the inductor 222continues to increase in magnitude to a peak value 415 (e.g., at t₆) asshown by the waveform 403. For example, the current-sensing signal 490continues to increase in magnitude to a peak value 417 (e.g., at t₆) asshown by the waveform 405. In another example, the feedback signal 486keeps at the low value 419 (e.g., 0) as shown by the waveform 401. Inyet another example, the demagnetization signal 442 keeps at the logiclow level (e.g., as shown by the waveform 409), and the switch 406remains open (e.g., off). In yet another example, the modulation signal458 keeps at the logic high level (e.g., as shown by the waveform 407).

According to yet another embodiment, at the beginning of the time periodT_(off2) (e.g., at t₆), the switch 224 is open (e.g., off). For example,at least part of the current (e.g., the current 278) flows from theinductor 222 to the one or more LEDs 280. In another example, thefeedback signal 486 changes from the low value 419 (e.g., 0) to a highvalue 413 (e.g., at t₆) as shown by the waveform 401. In yet anotherexample, the demagnetization signal 442 changes from the logic low levelto the logic high level (e.g., as shown by the waveform 409), whichindicates that the demagnetization process of the inductor 222 starts.In yet another example, the switch 406 is closed (e.g., on). In anotherexample, the gain stage 410 receives the stored current-sensing signal490, and outputs the amplified signal 446 to the amplifier 412 thatoutputs the integrated signal 450. In yet another example, themodulation signal 458 changes from the logic high level to the logic lowlevel (e.g., as shown by the waveform 407).

According to yet another embodiment, during the time period T_(demag2),the inductor 222 demagnetizes. For example, the magnitude of thefeedback signal 486 is kept higher than the low value 419 (e.g., asshown by the waveform 401). In another example, the current (e.g., thecurrent 278) that flows through the inductor 222 and the resistor 230decreases in magnitude to a low value 421 (e.g., at t₇) as shown by thewaveform 403. In yet another example, the current-sensing signal 490decreases in magnitude to a low value 423 (e.g., at t₇) as shown by thewaveform 405. In yet another example, the demagnetization signal 442keeps at the logic high level (e.g., as shown by the waveform 409), andthe switch 406 remains closed (e.g., on). In yet another example, theintegrated signal 450 keeps approximately at a magnitude 425 with asmall fluctuation (e.g., as shown by the waveform 411). In yet anotherexample, the modulation signal 458 keeps at the logic low level (e.g.,as shown by the waveform 407) during the time period T_(demag2). At theend of the time period T_(demag2), the feedback signal 486 abruptlydrops in magnitude as shown by the waveform 401, according to certainembodiments. For example, the demagnetization period of the inductor 222is detected by monitoring the feedback signal 486 at the terminal 270(e.g., FB).

In another embodiment, during the rest of the time period T_(off2)(e.g., after the demagnetization process of the inductor 222 ends att₇), the current that flows through the inductor 222 keeps at the lowvalue 421 (e.g., as shown by the waveform 403). For example, thecurrent-sensing signal 490 keeps at the low value 423 (e.g., as shown bythe waveform 405). In another example, the demagnetization signal 442keeps at the logic high level (e.g., as shown by the waveform 409), andthe switch 406 remains closed (e.g., on). In yet another example, theintegrated signal 450 keeps approximately at the magnitude 425 with asmall fluctuation (e.g., as shown by the waveform 411). In yet anotherexample, the modulation signal 458 keeps at the logic low level (e.g.,as shown by the waveform 407).

At the beginning of a next switching period (e.g., at t₈), a new cyclestarts according to certain embodiments. For example, the current thatflows through the inductor 222 increases in magnitude again (e.g., asshown by the waveform 403), and the current-sensing signal 490 increasesin magnitude again (e.g., as shown by the waveform 405). In anotherexample, the integrated signal 450 keeps approximately at the magnitude425 with a small fluctuation during the next switching period (e.g., asshown by the waveform 411) (e.g., because of a very limited loopbandwidth).

FIG. 5 is a simplified diagram showing a system for driving LEDsaccording to another embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The system 500 includes a regulation circuit 501, arectifying-and-filtering circuit 504, and a buck-boost switching circuit506. The rectifying-and-filtering circuit 504 includes a fuse 508, avaristor 510, a common-mode filtering inductor 512, two X capacitors 514and 516, a rectifying bridge 518, and a filtering capacitor 520. Thebuck-boost switching circuit 506 includes a primary winding 522, asecondary winding 552, a switch 524, a fly-back diode 526, a filteringcapacitor 528, a current-sensing resistor 530, and an output dummyresistor 532. The regulation circuit 501 includes a system controller502, three capacitors 534, 536 and 538, six resistors 540, 542, 544,546, 548 and 554, and a diode 550. The system controller 502 includessix terminals 560, 562, 564, 566, 568 and 570.

For example, a terminal of the resistor 530 and an end of the primarywinding 522 are each coupled to a chip ground 572. In another example,the system controller 502 is the same as the system controller 202. Inyet another example, the terminals 560, 562, 564, 566, 568 and 570 arethe same as the terminals 260, 262, 264, 266, 268 and 270, respectively.In yet another example, loop compensation is carried out internally inthe system controller 502, and the terminal 568 (e.g., COMP) is omitted.In yet another example, a switch 524 is a transistor.

According to one embodiment, the primary winding 522 has one terminalcoupled to the chip ground 572 and the other terminal coupled to one ormore LEDs 580. For example, the secondary winding 552 has one terminalcoupled to the chip ground 572, and the other terminal coupled to theterminal 570 (e.g., FB) through a resistor 544. In another example, theresistor 530 (e.g., R7) has one terminal coupled to the chip ground 572,and the other terminal coupled to the switch 524. In yet anotherexample, the diode 526 (e.g., D1) has one terminal (e.g., a cathodeterminal) coupled to the resistor 530, and the other terminal (e.g., ananode terminal) coupled to the one or more LEDs 580. In yet anotherexample, the terminal 564 (e.g., CS) is coupled to the chip ground 572through the capacitor 538 (e.g., C5), and coupled to both the resistor530 (e.g., R7) and the switch 524 through the resistor 548 (e.g., R5).In yet another example, the terminal 570 (e.g., FB) is coupled to thechip ground 572 through the resistor 546 (e.g., R4). In yet anotherexample, the terminal 562 (e.g., GATE) is coupled to the switch 524(e.g., at a gate terminal of the switch 524). In yet another example,the terminal 560 (e.g., GND) is coupled to the chip ground 572. Theresistor 548 (e.g., R5) and the capacitor 538 (e.g., C5) are omitted insome embodiments.

According to another embodiment, an AC input 574 is applied to therectifying-and-filtering circuit 504, which generates an input signal576. For example, the regulation circuit 501 receives the input signal576, and outputs a gate drive signal 588 through the terminal 562 (e.g.,GATE) to drive the switch 524. In another example, the switching circuit506 receives the input signal 576 for driving one or more LEDs 580. Inyet another example, a switching period of the system 500 includes anon-time period, T_(on), during which the switch 524 is closed (e.g.,on), and an off-time period, T_(off), during which the switch 524 isopen (e.g., off).

According to yet another embodiment, when the switch 524 is closed(e.g., on), a current 578 flows through the resistor 530 and atransformer that includes the primary winding 522 and the secondarywinding 552. For example, the transformer that includes the primarywinding 522 and the secondary winding 552 stores energy. In anotherexample, a voltage signal 590 is generated by the resistor 530. In yetanother example, the voltage signal 590 is proportional in magnitude tothe product of the current 578 and the resistance of the resistor 530.In yet another example, the voltage signal 590 is detected at theterminal 564 (e.g., CS) through the resistor 548.

When the switch 524 is open (e.g., off), the off-time period T_(off)begins, and a demagnetization process of the primary winding 522 startsaccording to some embodiments. For example, at least part of the current578 flows from the resistor 530 to the one or more LEDs 580 and flowsthrough the diode 526. In another example, the resistor 532 has a largeresistance, and a current 584 that flows through the one or more LEDs580 is close, in magnitude, to the current 578. In yet another example,a voltage signal 586 associated with the secondary winding 552 isdetected at the terminal 570 (e.g., FB) through a resistor divider thatincludes the resistors 544 and 546. In yet another example, the voltagesignal 586 is higher than the voltage of the chip ground 572 during thedemagnetization process of the primary winding 522. In yet anotherexample, after the demagnetization process of the primary winding 522 iscompleted, the voltage signal 586 decreases to a low value in magnitude.In yet another example, the system 500 operates with a broad range ofinputs and output loads, such as an output load of one or more LEDs(e.g., one LED).

In another embodiment, the peak value of the current 578 in eachswitching period of the system 500 is kept approximately constant bymonitoring the voltage signal 590 at the terminal 564 (e.g., CS). Forexample, the demagnetization period of the primary winding 522 isdetected by monitoring the voltage signal 586 at the terminal 570 (e.g.,FB). In another example, a switching period of the system 500 is N timesthe demagnetization period of the primary winding 522, where N is aratio larger than 1. Thus, an average magnitude of the current 584 thatflows through the one or more LEDs 580 can be determined based on thefollowing equation according to certain embodiments:

$\begin{matrix}{I_{LED} = {\frac{1}{2 \times N} \times \frac{V_{{TH}\; \_ \; {OC}}}{R\; 7}}} & \left( {{Equation}\mspace{14mu} 4} \right)\end{matrix}$

where I_(LED) represents the average magnitude of the current 584 thatflows through the one or more LEDs 580, N represents the ratio betweenthe switching period of the system 500 and the demagnetization period ofthe primary winding 522, V_(TH_OC) represents the peak value of thevoltage signal 590, and R7 represents the resistance of the resistor530. For example, the system controller 502 is the same as the systemcontroller 300, and the system controller 300 is used to replace thesystem controller 502 as part of the system 500. In yet another example,the system controller 502 is the same as the system controller 400, andthe system controller 400 is used to replace the system controller 502as part of the system 500.

FIG. 6 is a simplified diagram showing a system for driving LEDsaccording to yet another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The system 600 includes a regulation circuit 601, arectifying-and-filtering circuit 604, and a buck-boost switching circuit606. The rectifying-and-filtering circuit 604 includes a fuse 608, avaristor 610, a common-mode filtering inductor 612, two X capacitors 614and 616, a rectifying bridge 618, and a filtering capacitor 620. Thebuck-boost switching circuit 606 includes a buck-boost inductor 622, aswitch 624, a fly-back diode 626, a filtering capacitor 628, acurrent-sensing resistor 630, and an output dummy resistor 632. Theregulation circuit 601 includes a system controller 602, threecapacitors 634, 636 and 638, five resistors 640, 642, 644, 646 and 648,two diodes 650 and 652, and a Zener diode 654. The system controller 602includes six terminals 660, 662, 664, 666, 668 and 670.

For example, a terminal of the resistor 630 and a terminal of theinductor 622 are each coupled to a chip ground 672. In another example,the system controller 602 is the same as the system controller 202. Inyet another example, the terminals 660, 662, 664, 666, 668 and 670 arethe same as the terminals 260, 262, 264, 266, 268 and 270, respectively.In yet another example, loop compensation is carried out internally inthe system controller 602. In yet another example, the terminal 668(e.g., COMP) is omitted. In yet another example, the switch 624 is atransistor.

According to one embodiment, the inductor 622 (e.g., L2) has oneterminal coupled to the chip ground 672 and the other terminal coupledto one or more LEDs 680. For example, the resistor 630 (e.g., R7) hasone terminal coupled to the chip ground 672, and the other terminalcoupled to the switch 624. In another example, the diode 626 (e.g., D1)has one terminal (e.g., a cathode terminal) coupled to the chip ground672, and the other terminal (e.g., an anode terminal) coupled to the oneor more LEDs 680. In yet another example, the terminal 664 (e.g., CS) iscoupled to the chip ground 672 through the capacitor 638 (e.g., C5), andcoupled to both the resistor 630 (e.g., R7) and the switch 624 throughthe resistor 648 (e.g., R5). In yet another example, the terminal 670(e.g., FB) is coupled to the chip ground 672 through the resistor 646(e.g., R4), and coupled to the inductor 622 (e.g., L2) through theresistor 644 (e.g., R3) and the diode 652 (e.g., D3). In yet anotherexample, the terminal 662 (e.g., GATE) is coupled to the switch 624(e.g., at a gate terminal of the switch 624). In yet another example,the terminal 660 (e.g., GND) is coupled to the chip ground 672. Theresistor 648 (e.g., R5) and the capacitor 638 (e.g., C5) are omitted insome embodiments.

According to another embodiment, an AC input 674 is applied to therectifying-and-filtering circuit 604, which generates an input signal676. For example, the regulation circuit 601 receives the input signal676, and outputs a gate drive signal 688 through the terminal 662 (e.g.,GATE) to drive the switch 624. In another example, the buck-boostswitching circuit 606 receives the input signal 676 for driving one ormore LEDs 680. In yet another example, a switching period of the system600 includes an on-time period, T_(on), during which the switch 624 isclosed (e.g., on), and an off-time period, T_(off), during which theswitch 624 is open (e.g., off).

According to yet another embodiment, when the switch 624 is closed(e.g., on), a current 678 flows through the resistor 630 and theinductor 622. For example, the inductor 622 stores energy. In anotherexample, a voltage signal 690 is generated by the resistor 630. In yetanother example, the voltage signal 690 is proportional in magnitude tothe product of the current 678 and the resistance of the resistor 630.In yet another example, the voltage signal 690 is detected at theterminal 664 (e.g., CS) through the resistor 648.

According to yet another embodiment, when the switch 624 is open (e.g.,off), the off-time period T_(off) begins, and a demagnetization processof the inductor 622 starts. For example, at least part of the current678 flows from the inductor 622 to the one or more LEDs 680 and flowsthrough the diode 626. In another example, the resistor 632 has a largeresistance, and a current 684 that flows through the one or more LEDs680 is close, in magnitude, to the current 678. In yet another example,an output voltage signal 686 associated with the one or more LEDs 680 isdetected at the terminal 670 (e.g., FB) through a resistor divider thatincludes the resistor 644 and the resistor 646. In yet another example,the voltage signal 686 is higher than the voltage of the chip ground 672during the demagnetization process of the inductor 622. In yet anotherexample, after the demagnetization process of the inductor 622 iscompleted, the voltage signal 686 decreases to a low value in magnitude.In yet another example, the system 600 operates with a broad range ofinputs and output loads, such as an input range of AC 85V˜264V, and anoutput load of three or more LEDs.

According to yet another embodiment, the peak value of the current 678in each switching period of the system 600 is kept approximatelyconstant by monitoring the voltage signal 690 through the terminal 664(e.g., CS). For example, the demagnetization period of the inductor 622is detected by monitoring the voltage signal 686 through the terminal670 (e.g., FB). In another example, a switching period of the system 600is N times the demagnetization period of the inductor 622, where N is aratio larger than 1. Thus, an average magnitude of the current 684 thatflows through the one or more LEDs 680 can be determined based on thefollowing equation according to certain embodiments:

$\begin{matrix}{I_{LED} = {\frac{1}{2 \times N} \times \frac{V_{{TH}\; \_ \; {OC}}}{R\; 7}}} & \left( {{Equation}\mspace{14mu} 5} \right)\end{matrix}$

where I_(LED) represents the average magnitude of the current 684 thatflows through the one or more LEDs 680, N represents the ratio betweenthe switching period of the system 600 and the demagnetization period ofthe inductor 622, V_(TH_OC) represents the peak value of the voltagesignal 690, and R7 represents the resistance of the resistor 630. Forexample, the system controller 602 is the same as the system controller300, and the system controller 300 is used to replace the systemcontroller 602 as part of the system 600.

FIG. 7 is a simplified diagram showing a system for driving LEDsaccording to yet another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

The system 700 includes a regulation circuit 701, arectifying-and-filtering circuit 704, and a buck-boost switching circuit706. The rectifying-and-filtering circuit 704 includes a fuse 708, avaristor 710, a common-mode filtering inductor 712, two X capacitors 714and 716, a rectifying bridge 718, and a filtering capacitor 720. Thebuck-boost switching circuit 706 includes a primary winding 722, asecondary winding 752, a switch 724, a fly-back diode 726, a filteringcapacitor 728, a current-sensing resistor 730, and an output dummyresistor 732. The regulation circuit 701 includes a system controller702, three capacitors 734, 736 and 738, six resistors 740, 742, 744,746, 748 and 754, and a diode 750. The system controller 702 includessix terminals 760, 762, 764, 766, 768 and 770.

For example, a terminal of the resistor 730 and an end of the primarywinding 722 are each coupled to a chip ground 772. In another example,the system controller 702 is the same as the system controller 202. Inyet another example, the terminals 760, 762, 764, 766, 768 and 770 arethe same as the terminals 260, 262, 264, 266, 268 and 270, respectively.In yet another example, loop compensation is carried out internally inthe system controller 702, and the terminal 768 (e.g., COMP) is omitted.In yet another example, the switch 724 is a transistor.

According to one embodiment, the primary winding 722 has one terminalcoupled to the chip ground 772 and the other terminal coupled to one ormore LEDs 780. For example, the secondary winding 752 has one terminalcoupled to the chip ground 772, and the other terminal coupled to theterminal 770 (e.g., FB) through a resistor 744. In another example, theresistor 730 (e.g., R7) has one terminal coupled to the chip ground 772,and the other terminal coupled to the switch 724. In yet anotherexample, the diode 726 (e.g., D1) has one terminal (e.g., a cathodeterminal) coupled to the chip ground 772, and the other terminal (e.g.,an anode terminal) coupled to the one or more LEDs 780. In yet anotherexample, the terminal 764 (e.g., CS) is coupled to the chip ground 772through the capacitor 738 (e.g., C5), and coupled to both the resistor730 (e.g., R7) and the switch 724 through the resistor 748 (e.g., R5).In yet another example, the terminal 770 (e.g., FB) is coupled to thechip ground 772 through the resistor 746 (e.g., R4). In yet anotherexample, the terminal 762 (e.g., GATE) is coupled to the switch 724(e.g., at a gate terminal of the switch 724). In yet another example,the terminal 760 (e.g., GND) is coupled to the chip ground 772. Theresistor 748 (e.g., R5) and the capacitor 738 (e.g., C5) are omitted insome embodiments.

According to another embodiment, an AC input 774 is applied to therectifying-and-filtering circuit 704, which generates an input signal776. For example, the regulation circuit 701 receives the input signal776, and outputs a gate drive signal 788 through the terminal 762 (e.g.,GATE) to drive the switch 724. In another example, the buck-boostswitching circuit 706 receives the input signal 776 for driving one ormore LEDs 780. In yet another example, a switching period of the system700 includes an on-time period, T_(on), during which the switch 724 isclosed (e.g., on), and an off-time period, T_(off), during which theswitch 724 is open (e.g., off).

According to yet another embodiment, when the switch 724 is closed(e.g., on), a current 778 flows through the resistor 730 and atransformer that includes the primary winding 722 and the secondarywinding 752. For example, the transformer that includes the primarywinding 722 and the secondary winding 752 stores energy. In anotherexample, a voltage signal 790 is generated by the resistor 730. In yetanother example, the voltage signal 790 is proportional in magnitude tothe product of the current 778 and the resistance of the resistor 730.In yet another example, the voltage signal 790 is detected at theterminal 764 (e.g., CS) through the resistor 748.

According to yet another embodiment, when the switch 724 is open (e.g.,off), the off-time period T_(off) begins, and a demagnetization processof the primary winding 722 starts. For example, at least part of thecurrent 778 flows from the resistor 730 to the one or more LEDs 780 andflows through the diode 726. In another example, the resistor 732 has alarge resistance, and a current 784 that flows through the one or moreLEDs 780 is close, in magnitude, to the current 778. In yet anotherexample, a voltage signal 786 associated with the secondary winding 752is detected at the terminal 770 (e.g., FB) through a resistor dividerthat includes the resistors 744 and 746. In yet another example, thevoltage signal 786 is higher than the voltage of the chip ground 772during the demagnetization process of the primary winding 722. In yetanother example, after the demagnetization process of the primarywinding 722 is completed, the voltage signal 786 decreases to a lowvalue in magnitude. In yet another example, the system 700 operates witha broad range of inputs and output loads, such as an output load of oneor more LEDs (e.g., one LED).

According to yet another embodiment, the peak value of the current 778in each switching period of the system 700 is kept approximatelyconstant by monitoring the voltage signal 790 at the terminal 764 (e.g.,CS). For example, the demagnetization period of the primary winding 722is detected by monitoring the voltage signal 786 at the terminal 770(e.g., FB). In another example, a switching period of the system 700 isN times the demagnetization period of the primary winding 722, where Nis a ratio larger than 1. Thus, an average magnitude of the current 784that flows through the one or more LEDs 780 can be determined based onthe following equation according to certain embodiments:

$\begin{matrix}{I_{LED} = {\frac{1}{2 \times N} \times \frac{V_{{TH}\; \_ \; {OC}}}{R\; 7}}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$

where I_(LED) represents the average magnitude of the current 784 thatflows through the one or more LEDs 780, N represents the ratio betweenthe switching period of the system 700 and the demagnetization period ofthe primary winding 722, V_(TH_OC) represents the peak value of thevoltage signal 790, and R7 represents the resistance of the resistor730. For example, the system controller 702 is the same as the systemcontroller 300, and the system controller 300 is used to replace thesystem controller 702 as part of the system 700.

According to another embodiment, a system for regulating one or morecurrents includes a system controller, an inductor, a first resistor, aswitch and a first diode. The system controller includes a firstcontroller terminal and a ground terminal, the system controller beingconfigured to output a drive signal at the first controller terminal.The inductor includes a first inductor terminal and a second inductorterminal, the first inductor terminal being coupled to the groundterminal, the second inductor terminal being coupled to one or morelight emitting diodes. The first resistor includes a first resistorterminal and a second resistor terminal, the first resistor terminalbeing coupled to the ground terminal. The switch is configured toreceive the drive signal and coupled to the second resistor terminal.Moreover, the first diode includes a first diode terminal and a seconddiode terminal and coupled to the first resistor, the second diodeterminal being coupled to the one or more light emitting diodes. Forexample, the system is implemented according to at least FIG. 2, FIG.3(a), FIG. 3(b), FIG. 4(a), FIG. 4(b), and/or FIG. 6.

According to yet another embodiment, a system for regulating one or morecurrents includes a system controller, a transformer, a first resistor,a switch, and a first diode. The system controller includes a firstcontroller terminal and a ground terminal, the system controller beingconfigured to output a drive signal at the first controller terminal.The transformer includes a primary winding and a secondary winding, theprimary winding including a first winding terminal and a second windingterminal, the secondary winding including a third winding terminal and afourth winding terminal, the first winding terminal being coupled to theground terminal, the second winding terminal being coupled to one ormore light emitting diodes, the third winding terminal being coupled tothe ground terminal. The first resistor includes a first resistorterminal and a second resistor terminal, the first resistor terminalbeing coupled to the ground terminal. The switch is configured toreceive the drive signal and coupled to the second resistor terminal.Additionally, the first diode includes a first diode terminal and asecond diode terminal and coupled to the first resistor, the seconddiode terminal being coupled to the one or more light emitting diodes.For example, the system is implemented according to at least FIG. 3(a),FIG. 3(b), FIG. 4(a), FIG. 4(b), FIG. 5 and/or FIG. 7.

According to yet another embodiment, a system for regulating one or morecurrents includes a system controller that is configured to output adrive signal to a switch and to receive a sensed signal from a resistorconnected to the switch and an inductor, the resistor and the inductorbeing connected directly or indirectly to one or more light emittingdiodes. Additionally, the drive signal is associated with one or moreswitching periods, each of the one or more switching periods includingan on-time period for the switch and an off-time period for the switch.Moreover, each of the one or more switching periods is equal to a ratiomultiplied by a demagnetization period for a demagnetization processassociated with the inductor, the ratio being larger than 1.Furthermore, a first current flowing through the one or more lightemitting diodes is proportional to a peak magnitude of the sensed signalwithin each of the one or more switching periods. For example, thesystem is implemented according to at least FIG. 2, FIG. 5, FIG. 6,and/or FIG. 7.

According to yet another embodiment, a system for regulating one or morecurrents includes a modulation-and-drive component, a sample-and-holdcomponent, an amplification component, an error amplifier, and acomparator. The modulation-and-drive component is configured to output adrive signal to a switch, the drive signal being associated with atleast one switching period including an on-time period for the switchand a demagnetization period for a demagnetization process. Thesample-and-hold component is configured to receive a sensed signalrelated to a current flowing through the switch, sample the sensedsignal at the middle of the on-time period, and hold the sampled sensedsignal. The amplification component is configured to receive the heldand sampled sensed signal during the demagnetization period and generatean amplified signal. In addition, the error amplifier is configured toreceive the amplified signal during the demagnetization period andgenerate, with at least a first capacitor, an integrated signal.Moreover, the comparator is configured to receive at least theintegrated signal and output a comparison signal to themodulation-and-drive component based on at least information associatedwith the integrated signal. For example, the system is implementedaccording to at least FIG. 2, FIG. 3(a), FIG. 3(b), FIG. 5, FIG. 6,and/or FIG. 7.

In another embodiment, a system for regulating one or more currentsincludes a modulation-and-drive component, a signal-holding component,an amplification component, an error amplifier, and a comparator. Themodulation-and-drive component is configured to output a drive signal toa switch, the drive signal being associated with at least one switchingperiod including an on-time period for the switch and a demagnetizationperiod for a demagnetization process. The amplification component isconfigured to, during the demagnetization period, receive a sensedsignal related to a first current flowing through the switch andgenerate an amplified signal. Additionally, the error amplifier isconfigured to receive the amplified signal during the demagnetizationperiod and generate, with at least a first capacitor, an integratedsignal. Moreover, the comparator is configured to receive at least theintegrated signal and output a comparison signal to themodulation-and-drive component based on at least information associatedwith the integrated signal. For example, the system is implementedaccording to at least FIG. 2, FIG. 4(a), FIG. 4(b), and/or FIG. 5.

In yet another embodiment, a method for regulating one or more currentsincludes receiving a sensed signal from a resistor connected to a switchand an inductor, and processing information associated with the sensedsignal. In addition, the method includes generating a drive signal forthe switch based on at least information associated with the sensedsignal, processing information associated with the drive signal, andgenerating a current flowing through one or more light emitting diodesbased on at least information associated with the drive signal, the oneor more light emitting diodes being connected directly or indirectly tothe resistor and the inductor. Further, the drive signal is associatedwith one or more switching periods, each of the one or more switchingperiods including an on-time period for the switch and an off-timeperiod for the switch. Each of the one or more switching periods isequal to a ratio multiplied by a demagnetization period for ademagnetization process associated with the inductor, the ratio beinglarger than 1. Moreover, the current is proportional to a peak magnitudeof the sensed signal within each of the one or more switching periods.For example, the method is implemented according to at least FIG. 2,FIG. 5, FIG. 6, and/or FIG. 7.

In yet another embodiment, a method for regulating one or more currentsincludes generating a drive signal for a switch, the drive signal beingassociated with at least one switching period including an on-timeperiod for the switch and a demagnetization period for a demagnetizationprocess. The method further includes receiving a sensed signal relatedto a current flowing through the switch, processing informationassociated with the sensed signal, and sampling the sensed signal at themiddle of the on-time period. In addition, the method includes holdingthe sampled sensed signal, receiving the held and sampled sensed signalduring the demagnetization period, and processing information associatedwith the received held and sampled sensed signal. The method alsoincludes generating an amplified signal based on at least informationassociated with the received held and sampled sensed signal, receivingthe amplified signal, and processing information associated with theamplified signal. Furthermore, the method includes generating anintegrated signal based on at least information associated with theamplified signal, receiving at least the integrated signal, processinginformation associated with the integrated signal, and generating acomparison signal based on at least information associated with theintegrated signal. For example, the method is implemented according toat least FIG. 2, FIG. 3(a), FIG. 3(b), FIG. 5, FIG. 6 and/or FIG. 7.

In yet another embodiment, a method for regulating one or more currentsincludes generating a drive signal for a switch, the drive signal beingassociated with at least one switching period including an on-timeperiod for the switch and a demagnetization period for a demagnetizationprocess. Additionally, the method includes receiving a sensed signalrelated to a current flowing through the switch during thedemagnetization period, processing information associated with thereceived sensed signal, and generating an amplified signal based oninformation associated with the received sensed signal. The method alsoincludes receiving the amplified signal, processing informationassociated with the amplified signal, and generating an integratedsignal based on at least information associated with the amplifiedsignal. Moreover, the method includes receiving at least the integratedsignal, processing information associated with the integrated signal,generating a comparison signal based on at least information associatedwith the integrated signal, and receiving the comparison signal. Forexample, the method is implemented according to at least FIG. 2, FIG.4(a), FIG. 4(b), and/or FIG. 5.

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

1.-9. (canceled)
 10. A system for regulating one or more currents, thesystem comprising: a system controller including a first controllerterminal and a ground terminal, the system controller being configuredto output a drive signal at the first controller terminal; a transformerincluding a primary winding and a secondary winding, the primary windingincluding a first winding terminal and a second winding terminal, thesecondary winding including a third winding terminal and a fourthwinding terminal, the first winding terminal being coupled to the groundterminal, the second winding terminal being coupled to one or more lightemitting diodes, the third winding terminal being coupled to the groundterminal; a first resistor including a first resistor terminal and asecond resistor terminal, the first resistor terminal being coupled tothe ground terminal; a switch configured to receive the drive signal andcoupled to the second resistor terminal; and a first diode including afirst diode terminal and a second diode terminal and coupled to thefirst resistor, the second diode terminal being coupled to the one ormore light emitting diodes.
 11. The system of claim 10 wherein: thesecond resistor terminal is coupled to the first diode terminal; and thefirst diode terminal is coupled to the switch.
 12. The system of claim10 wherein: the first resistor terminal is coupled to the first diodeterminal; and the first diode terminal is coupled to the groundterminal. 13.-29. (canceled)